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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Optics and materials considerations for a laser-propelled lightsail

The principles of a laser-propelled lightsail for an interstellar probe are discussed. The feasibility of a laser-propelled-lightsail round-trip interstellar mission proposed by Forward (1984) is examined, with special attention given to the issues of optics and materials. It is shown that the large lens and a high lens/target distance required by such a mission result in optical difficulties, requiring positioning tolerance for the 1000-km-diam lens of only 3 m, which is unlikely to be achievable. Techniques and sail materials that would reduce this problem are suggested, including the use of LiF and CaF2 quarter-wave dielectric films and the use of many intermediate lenses spaced between the probe and the source. It is pointed out that, as sail materials, the quarter-wavelength dielectric films have significant advantages over metals.

Landis, Geoffrey A.↗
NASA NTRS1989

The cavity heat pipe Stirling receiver for space solar dynamics

The receiver/storage unit for the low-earth-orbiting Stirling system is discussed. The design, referred to as the cavity heat pipe (CHP), has been optimized for minimum specific mass and volume width. A specific version of this design at the 7-kWe level has been compared to the space station Brayton solar dynamic design. The space station design utilizes a eutectic mixture of LiF and CaF2. Using the same phase change material, the CHP has been shown to have a specific mass of 40 percent and a volume of 5 percent of that of the space station Brayton at the same power level. Additionally, it complements the free-piston Stirling engine in that it also maintains a relatively flat specific mass down to at least 1 kWe. The technical requirements, tradeoff studies, critical issues, and critical technology experiments are discussed.

Kesseli, James B.↗
NASA NTRS1990

A study of the scintillation light induced in liquid xenon by electrons and alpha particles

The time dependence and the intensity of the primary scintillation light in liquid Xe excited by Am-241 alpha particles and Bi-207 internal-conversion electrons were measured at different electric-field strengths. High-purity liquid Xe was used to fill a parallel-plate ionization chamber equipped with a CaF2 window coupled to a UV-sensitive photomultiplier tube. The effect of the specific ionization density on the scintillation light and the time correlation between the light signal and the charge signal is reported. It is demonstrated that the fast scintillation signal produced in liquid Xe by an ionizing particle provides an ideal trigger in a detector aiming at a complete three-dimensional event reconstruction with an excellent background rejection capability.

Aprile, Elena↗
NASA NTRS1991

Multi-dimensional modeling of a thermal energy storage canister

The Solar Dynamic Power Module being developed for Space Station Freedom uses a eutectic mixture of LiF-CaF2 phase change material (PCM) contained in toroidal canisters for thermal energy storage. Presented are the results from heat transfer analyses of a PCM containment canister. One and two dimensional finite difference computer models are developed to analyze heat transfer in the canister walls, PCM, void, and heat engine working fluid coolant. The modes of heat transfer considered include conduction in canister walls and solid PCM, conduction and pseudo-free convection in liquid PCM, conduction and radiation across PCM vapor filled void regions, and forced convection in the heat engine working fluid. Void shape, location, growth or shrinkage (due to density difference between the solid and liquid PCM phases) are prescribed based on engineering judgment. The PCM phase change process is analyzed using the enthalpy method. The discussion of the results focuses on how canister thermal performance is affected by free convection in the liquid PCM and void heat transfer. Characterizing these effects is important for interpreting the relationship between ground-based canister performance (in 1-g) and expected on-orbit performance (in micro-g). Void regions accentuate canister hot spots and temperature gradients due to their large thermal resistance. Free convection reduces the extent of PCM superheating and lowers canister temperatures during a portion of the PCM thermal charge period. Surprisingly small differences in canister thermal performance result from operation on the ground and operation on-orbit. This lack of a strong gravity dependency is attributed to the large contribution of container walls in overall canister energy redistribution by conduction.

Kerslake, Thomas W.↗
NASA NTRS1990

TEMPUS: First results

The electromagnetic levitation facility, TEMPUS, developed by Dornier is designed to operate under microgravity conditions. Compared to terrestrial levitation, microgravity offers the possibility to melt and undercool in ultra high vacuum, thereby, providing an ultra clean environment. The technical concept of the TEMPUS facility was tested on two KC 135 flights and in the Texus 22 mission. Preparative investigations concerning the coil system and the heating and positioning efficiencies were carried out in the TEMPUS laboratory version. Furthermore, temperature-time profiles were determined under various boundary conditions. As a consequence of processing liquid metals under UHV, correct temperature measurement arises as the most critical problem. Experiences with experiments in the TEMPUS laboratory module show that due to the evaporation losses of the sample, the transmission of the CaF2 shielding windows changes drastically during the processing time. The investigation of the effect of contamination on pyrometry and the development of alternative evaporation shielding methods were initiated. During the second KC 135 flight, it was possible to heat up and melt an FeNi sample under He atmosphere. Oscillations of the molten sample, which were excited by switching out the magnetic heating field, could be detected and afterwards analyzed. From the frequency of these oscillations the surface tension of the sample material could be derived. The measurement of the surface tension and viscosity of an undercooled metal is proposed for TEMPUS on IML-2. This document is presented in view graph form.

Neuhaus, P.↗
NASA NTRS1991

Space environmental effects on coated optics

Several multilayer coated mirror designs developed for potential space applications were tested on the Long Duration Exposure Facility (LDEF) along with single layer witness coatings deposited on fused silica and a coated CaF2 window. Performance requirements included high mirror reflectivity, low absorption, low scatter, environmental durability, and radiation hardness. The designs were selected in screening tests using combined electron, proton, and simulated solar UV radiation. The purpose of the space test was to validate the above test results and determine the effects of atomic oxygen and contamination on mirror performance.

Donovan, T. M.↗
NASA NTRS1990

Two-dimensional model of a Space Station Freedom thermal energy storage canister

The Solar Dynamic Power Module being developed for Space Station Freedom uses a eutectic mixture of LiF-CaF2 phase change salt contained in toroidal canisters for thermal energy storage. Results are presented from heat transfer analyses of the phase-change salt containment canister. A 2-D, axisymmetric finite-difference computer program which models the canister walls, salt, void, and heat engine working fluid coolant was developed. Analyses included effects of conduction in canister walls and solid salt, conduction and free convection in liquid salt, conduction and radiation across salt vapor filled void regions, and forced convection in the heat engine working fluid. Void shape, location, and growth or shrinkage (due to density difference between the solid and liquid salt phases) were prescribed based on engineering judgement. The salt phase change process was modeled using the enthalpy method. Discussion of results focuses on the role of free-convection in the liquid salt on canister heat transfer performance. This role is shown to be important for interpreting the relationship between groundbased canister performance (in 1-g) and expected on-orbit performance (in micro-g). Attention is also focused on the influence of void heat transfer on canister wall temperature distributions. The large thermal resistance of void regions is shown to accentuate canister hot spots and temperature gradients.

Kerslake, Thomas W.↗
NASA NTRS1991

Atomic force microscope studies of fullerene films - Highly stable C60 fcc (311) free surfaces

Atomic force microscopy and X-ray diffractometry were used to study 1500 A-thick films of pure C60 grown by sublimation in ultrahigh vacuum onto a CaF2 (111) substrte. Topographs of the films did not reveal the expected close-packed structures, but they showed instead large regions that correspond to a face-centered cubic (311) surface and distortions of this surface. The open (311) structure may have a relatively low free energy because the low packing density contributes to a high entropy of the exposed surface.

Snyder, Eric J.↗
NASA NTRS1992

Stress versus temperature dependence of activation energies for creep

The activation energy for creep at low stresses and elevated temperatures is associated with lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from dislocation climb to obstacle-controlled dislocation glide. Along with this change in deformation mechanism occurs a change in the activation energy. When the rate controlling mechanism for deformation is obstacle-controlled dislocation glide, it is shown that a temperature-dependent Gibbs free energy does better than a stress-dependent Gibbs free energy in correlating steady-state creep data for both copper and LiF-22mol percent CaF2 hypereutectic salt.

Freed, A. D.↗
NASA NTRS1992

Lunar mining of oxygen using fluorine

An important aspect of lunar mining will be the extraction of volatiles, particularly oxygen, from lunar rocks. Thermodynamic data show that oxygen could readily be recovered by fluorination of abundant lunar anorthite, CaAl2Si2O8. Fluorine is the most reactive element, and the only reagent able to extract 100 percent of the oxygen from any mineral, yet it can safely be stored or reacted in nickel or iron containers. The general fluorination reaction, mineral + 2F2 = mixed fluorides = O2, has been used for more than 30 years at a laboratory scale by stable-isotope geochemists. For anorthite, metallic Al and Si may be recovered from the mixed fluorides by Na-reduction, and CaO via exchange with Na2O; the resulting NaF may be recycled into F2 and Na by electrolysis, using lanthanide-doped CaF2 as the inert anode.

Burt, Donald M.↗
NASA NTRS1993

Ultraviolet Imaging Spectrometer

Wide-field imaging systems equipped with objective prisms or gratings have had a long history of utility in groundbased observations of meteors and comets. Deployment of similar instruments from low Earth orbit would allow the first UV observations of meteors. This instrument can be used for comets and Lyman alpha coronae of Earth-orbit-crossing asteroids. A CaF2 prism imaging spectrograph designed for stellar observations was used aboard Skylab to observe Comet Kohoutek (1973f), but its 1300-A cut-off precluded Lyman alpha images and it was not used for observation of meteors. Because the observation of the UV spectrum of a meteor has never been attempted, researchers are denied the opportunity to obtain composition information from spectra at those wavelengths. We propose construction of a flight instrument functioning in the 1100-3200 A spectral range that is suitable for a dedicated satellite ('Quick Star') or as a space-station-attached payload. It can also be an autonomous package in the space shuttle cargo bay.

Wdowiak, T. J.↗
NASA NTRS1991

Catalog of infrared and cryo-optical properties for selected materials

This report will describe the status of an effort to catalog the refractive index, absorption, reflectance and transmittance of selected IR transmitting materials over the wavelength range from 1 to 1000 microns, and at temperatures from 300 to about 2 K. Data are presented for LiF, CaF2, BaF2, KBr, and TlBr, as well as for KRS-5 (TlBr-I) and KRS-6 (TlBr-Cl). A cryooptical measurements facility at NASA-Goddard, which has been used to generate some of the cataloged data, is also described.

Heaney, James B.↗
NASA NTRS1997

Modeling Cyclic Phase Change and Energy Storage in Solar Heat Receivers

Numerical results pertaining to cyclic melting and freezing of an encapsulated phase change material (PCM), integrated into a solar heat receiver, have been reported. The cyclic nature of the present melt/freeze problem is relevant to latent heat thermal energy storage (LHTES) systems used to power solar Brayton engines in microgravity environments. Specifically, a physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) project was developed and results compared with available experimental data. Multi-conjugate effects such as the convective fluid flow of a low-Prandtl-number fluid, coupled with thermal conduction in the phase change material, containment tube and working fluid conduit were accounted for in the model. A single-band thermal radiation model was also included to quantify reradiative energy exchange inside the receiver and losses through the aperture. The eutectic LiF-CaF2 was used as the phase change material (PCM) and a mixture of He/Xe was used as the working fluid coolant. A modified version of the computer code HOTTube was used to generate results for comparisons with GTD data for both the subcooled and two-phase regimes. While qualitative trends were in close agreement for the balanced orbit modes, excellent quantitative agreement was observed for steady-state modes.

Hall, Carsie A., III↗
NASA NTRS1997

Parametric Analysis of Cyclic Phase Change and Energy Storage in Solar Heat Receivers

A parametric study on cyclic melting and freezing of an encapsulated phase change material (PCM), integrated into a solar heat receiver, has been performed. The cyclic nature of the present melt/freeze problem is relevant to latent heat thermal energy storage (LHTES) systems used to power solar Brayton engines in microgravity environments. Specifically, a physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) project was developed. Multi-conjugate effects such as the convective fluid flow of a low-Prandtl-number fluid, coupled with thermal conduction in the phase change material, containment tube and working fluid conduit were accounted for in the model. A single-band thermal radiation model was also included to quantify reradiative energy exchange inside the receiver and losses through the aperture. The eutectic LiF-CaF2 was used as the phase change material (PCM) and a mixture of He/Xe was used as the working fluid coolant. A modified version of the computer code HOTTube was used to generate results in the two-phase regime. Results indicate that parametric changes in receiver gas inlet temperature and receiver heat input effects higher sensitivity to changes in receiver gas exit temperatures.

Hall, Carsie A., III↗
NASA NTRS1962

Lubricating Properties of Ceramic-Bonded Calcium Fluoride Coatings on Nickel-Base Alloys from 75 to 1900 deg F

The endurance life and the friction coefficient of ceramic-bonded calcium fluoride (CaF2) coatings on nickel-base alloys were determined at temperatures from 75 F to 1900 F. The specimen configuration consisted of a hemispherical rider (3/16-in. rad.) sliding against the flat surface of a rotating disk. Increasing the ambient temperature (up to 1500 F) or the sliding velocity generally reduced the friction coefficient and improved coating life. Base-metal selection was critical above 1500 F. For instance, cast Inconel sliding against coated Inconel X was lubricated effectively to 1500 F, but at 1600 F severe blistering of the coatings occurred. However, good lubrication and adherence were obtained for Rene 41 sliding against coated Rene 41 at temperatures up to 1900 F; no blisters developed, coating wear life was fairly good, and the rider wear rate was significantly lower than for the unlubricated metals. Friction coefficients were 0.12 at 1500 F, 0.15 at 1700 F, and 0.17 at 1800 F and 1900 F. Because of its ready availability, Inconel X appears to be the preferred substrate alloy for applications in which the temperature does not exceed 1500 F. Rene 41 would have to be used in applications involving higher temperatures. Improved coating life was derived by either preoxidizing the substrate metals prior to the coating application or by applying a very thin (less than 0.0002 in.) burnished and sintered overlay to the surface of the coating. Preoxidation did not affect the friction coefficient. The overlay generally resulted in a higher friction coefficient than that obtained without the overlay. The combination of both modifications resulted in longer coating life and in friction coefficients intermediate between those obtained with either modification alone.

Sliney, Harold E.↗
NASA NTRS1999

Swift: A Widefield Imaging Fabry Perot for Sofia

Contract was to pursue feasibility studies of the SOFIA Widefield Imaging Fabry-Perot (SWIFT). SWIFT was proposed as a two color 18 to 40 microns imaging Fabry-Perot that utilized two Rockwell/Boeing 256 x 256 pixel Si:Sb BIBs as detective devices. The colors were to be split between 26 and 30 microns using a MgO dichroic. The resolution achieving devices were to be a pair of cryogenic fully tunable scanning Fabry-Perot interferometers (FPIs), two in each band. For high resolving powers, a third, fixed FPI is inserted into the beam. The FPI mirrors were to be made of free standing metal mesh. We also proposed to look into a long wavelength (40 to 210 microns) band during the feasibility study period. We produced a proposal to USRA, submitted in July 1997 that substantially refined our ideas. We decided the long wavelength science was compelling, so the baseline wavelength coverage for SWIFT was widened to 17 to 205 microns. Under typical operations, we proposed to simultaneously image in two bands: 22 to 38 microns, and 50 to 205 microns. The bands were to be split by a cold CaF2 dichroic. The short wavelength (SW) band was to employ a 256 x 256 pixel Boeing/Rockwell Si:Sb BIB array, and the long wavelength (LW) band was to employ a Goddard 6 x 32 (upgradable to 32 x 32) element array of monolithic silicon "pop-up" bolometers as detective devices. The two color capability doubled the data taking efficiency, and ensured "perfect" registration between the images obtained in each band. For the SW band, the beam was to be fully sampled (0.7" pixels, 1.4 in. beam) at 17 microns, and over sampled at longer wavelengths. Even so, SWIFT has a very large (3 ft x 3 ft) field of view. To match the SW and LW fields of view (initially in one dimension only, but in 2-dimensions with 32 x 32 upgrade), SWIFT was to under sample at 63 microns (5.6 in pixels, 5.2 in beam) resulting in a 0.56 x 3 in (upgrade to 3 in x 3 in) field of view. Each band has both Lo-Res (R triple bond lambda/Delta(lambda) approx. 30 to 200) and Hi-Res (R approx. 1000 up to 10(exp 5)) modes, that can be changed in less than a minute. Spectral resolution is obtained with four identical cryogenic, fully tunable, scanning FPIS, two in each band, plus a set of fixed order FPI that can be rotated into the beam for good spectral purity at the highest resolving powers. SWIFT was proposed to explore three primary topics of scientific interest: 1. Protostars, Young Stellar Objects, and Protoplanetary Disks. 2. The Galactic Center. 3. External Galaxies.

Stacey, Gordon J.↗
NASA NTRS1998

Far Ultraviolet Refractive Index of Optical Materials for Solar Blind Channel (SBC) Filters for HST Advanced Camera for Surveys

Refractive index measurements using the minimum deviation method have been carried out for prisms of a variety of far ultraviolet optical materials used in the manufacture of Solar Blind Channel (SBC) filters for the HST Advanced Camera for Surveys (ACS). Some of the materials measured are gaining popularity in a variety of high technology applications including high power excimer lasers and advanced microlithography optics operating in a wavelength region where high quality knowledge of optical material properties is sparse. Our measurements are of unusually high accuracy and precision for this wavelength region owing to advanced instrumentation in the large vacuum chamber of the Diffraction Grating Evaluation Facility (DGEF) at Goddard Space Flight Center (GSFC). Index values for CaF2, BaF2, LiF, and far ultraviolet grades of synthetic sapphire and synthetic fused silica are reported and compared with values from the literature.

Leviton, Douglas B.↗
NASA NTRS2002

Investigation of Thermal Processing on the Properties of PS304: A Solid Lubricant Coating

The effect of thermal processing on PS304, a solid lubricant coating, was investigated. PS304 is a plasma sprayed solid lubricant consisting of 10% Ag and 10% BaF2 and CaF2 in a eutectic mixture for low and high temperature lubricity respectively. In addition, PS304 contains 20% Cr2O3 for increased hardness and 60% NiCr which acts as a binder. All percents are in terms of weight not volume. Previous research on thermal processing (NAG3-2245) of PS304 revealed that substrate affected both the pre- and post-anneal hardness of the plasma spray coating. The objective of this grant was to both quantify this effect and determine whether the root cause was an artifact of the substrate or an actual difference in hardness due to interaction between the substrate and the coating. In addition to clarifying past research developments new data was sought in terms of coating growth due to annealing.

Benoy, Patricia A.↗